Patent Document 1 discloses a filter that is floatable on a liquid. This filter includes a filter case and, formed in the filter case, an air release hole provided with a float that moves up and down in accordance with a height of a liquid level inside an inflow space, and an air reservoir that contains air in a sealed state inside the inflow space when the float is blocking an opening of the air release hole. The liquid level lowers with an increase in the air accumulated in the air reservoir, thereby separating the float from the opening and allowing a portion of the air in the air reservoir to discharge via the air release hole.
The invention described in Patent Document 1 is configured to filter a fuel of a power machine, and prevent the occurrence of defects (engine knocking and engine stall, for example) caused by air contained in a fuel that passed through a filter.